Each test method has its advantages and disadvantages. RT is not the examination of choice if the discontinuities are related to weld profile. Undercut, overlap, laminations, etc. are best evaluated by visual examination. Subsurface porosity, root cracks in a pipe joint, slag inclusions, etc. are best evaluated using RT.
Unless boroscopic examination is included in the project specifications, I would resist using it. The piping code is pretty specific about what examinations and test methods are to be used. B31.3 is also specific with regards to using Section V for the qualification of inspection personnel and technique. Visual examination is limited to what you can seen by eye. The use of boroscopes, fiberscopes, etc. is not considered to be direct visual examination and beyond the scope of visual examination.
Rather than dancing around the subject, have you looked at Section V to see what they have to say on the subject of visual examination?
Al